Enhanced left frontal involvement during novel metaphor comprehension in schizophrenia: evidence from functional neuroimaging

The neural basis involved in novel metaphor comprehension in schizophrenia is relatively unknown. Fourteen people with schizophrenia and fourteen controls were scanned while they silently read novel metaphors, conventional metaphors, literal expressions, and meaningless word-pairs. People with schizophrenia showed reduced comprehension of both novel and conventional metaphors. Furthermore, while controls showed enhanced brain activation in right inferior frontal gyrus (IFG) for novel metaphors versus meaningless word-pairs, people with schizophrenia showed an over-activation of left IFG and middle frontal gyrus (MFG). Direct comparison between the groups revealed greater activation in left precuneus for both novel metaphors and literal expressions vs. baseline for individuals with schizophrenia. Direct comparison for novel metaphors vs. literal expressions also revealed increased activation for individuals with schizophrenia in left MFG. These results suggest that the inefficient processing of novel metaphors in schizophrenia involves compensatory recruitment of additional brain regions that include the left MFG and left precuneus.

Right hemisphere sensitivity to novel metaphoric relations: application of the signal detection theory

The present study used the signal detection theory to test the hypothesis that the right hemisphere (RH) is more sensitive than the left hemisphere (LH) to the distant semantic relations in novel metaphoric expressions. In two divided visual field experiments, sensitivity (d') and criterion (beta) were calculated for responses to different types of word pairs. In the first experiment, subjects were presented with unfamiliar two-word novel metaphoric expressions ("signal") and unrelated word-pairs ("noise"). In the second experiment, literal expressions ("signal") and unrelated word pairs ("noise") were presented. In line with the Coarse Semantic Coding Theory [Beeman, M. (1998). Coarse semantic coding and discourse comprehension. In: M. Beeman & C. Chiarello (Eds.). Right hemisphere language comprehension: Perspectives from cognitive neuroscience. Mahwah, NJ: Erlbaum, pp. 255-284.] as well as with the Graded Salience Hypothesis [Giora, R. (2003). On our mind: Salience, context and figurative language. New York: Oxford University Press.], the findings suggest that the RH is more sensitive than the LH to unfamiliar metaphoric relations. Furthermore, this RH advantage in processing distant semantic relations did not extend to familiar semantic relations.

An fMRI investigation of the neural correlates underlying the processing of novel metaphoric expressions

The neural networks associated with processing related pairs of words forming literal, novel, and conventional metaphorical expressions and unrelated pairs of words were studied in a group of 15 normal adults using fMRI. Subjects read the four types of linguistic expressions and decided which relation exists between the two words (metaphoric, literal, or unrelated). According to the Graded Salience Hypothesis (GSH, ), which predicts a selective RH involvement in the processing of novel, nonsalient meanings, it is primarily the degree of meaning salience of a linguistic expression rather than literality or nonliterality, which modulates the degree of left hemisphere (LH) and right hemisphere (RH) processing of metaphors. In the present study, novel metaphorical expressions represented the nonsalient interpretations, whereas conventional metaphors and literal expressions represented the salient interpretations. A direct comparison of the novel metaphors vs. the conventional metaphors revealed significantly stronger activity in right posterior superior temporal sulcus, right inferior frontal gyrus, and left middle frontal gyrus. These results support the GSH and suggest a special role for the RH in processing novel metaphors. Furthermore, the right PSTS may be selectively involved in verbal creativity.

The role of the right cerebral hemisphere in processing novel metaphoric expressions taken from poetry: a divided visual field study

Previous research suggests that the right hemisphere (RH) may contribute uniquely to the processing of metaphoric language. However, most studies have focused on familiar metaphoric expressions. The present study used the divided visual field paradigm to examine the role of the right cerebral hemisphere in processing novel metaphoric expressions taken from poetry. In two experiments, participants were presented with four types of word pairs, literal, conventional metaphoric and novel metaphoric expressions and unrelated word pairs, and asked to perform a semantic judgment task. Two different SOAs: 400 and 1100 ms were used. The results of both experiments showed that responses to LVF/RH presented target words were more accurate and faster than responses to RVF/LH target words for novel metaphoric expressions, but not for other types of word pairs. These results support previous research indicating that during word recognition, the RH activates a broader range of related meanings than the LH, including novel, nonsalient meanings. The findings thus suggest that the RH may be critically involved in at least one important component of novel metaphor comprehension, i.e., the integration of the individual meanings of two seemingly unrelated concepts into a meaningful metaphoric expression.

The role of the right hemisphere in processing nonsalient metaphorical meanings: Application of Principal Components Analysis to fMRI data

Some researches indicate that the right hemisphere (RH) has a unique role in comprehending the figurative meaning of metaphors whereas the results of other studies do not support the notion of a selective role for the RH in accessing metaphorical meanings. The present research used fMRI technology to test a theoretical explanation of the above conflicting findings. This theoretical account is derived from the Graded Salience Hypothesis (GSH) [Giora, R. (1997). Understanding figurative and literal language: the Graded Salience Hypothesis. Cognitive Linguistics, 7, 183-206; Giora, R. (2003). On our mind: Salience, context and figurative language. New York: Oxford University Press], according to which the degree of meaning salience, rather than literality or nonliterality primarily affects differences between the LH and RH in linguistic processing. Thus, the GSH predicts a selective RH involvement in comprehension of novel, nonsalient metaphoric meanings and LH involvement in the comprehension of conventional, salient metaphoric meanings. Fifteen normal adults participated in a block designed fMRI experiment that compared the patterns of brain activation induced by processing the meanings of literal, conventional metaphoric, novel metaphoric and unrelated word pairs. The subjects performed a semantic judgment task. We applied the Principal Components Analysis (PCA) technique in order to find different functional networks corresponding to the different stimuli. Our results, obtained from PCA of the fMRI data indicate that the right homologue of Wernicke's area has a special role in processing novel metaphors. We suggest that a unique network, consisting of the right homologue of Wernicke's area, right and left premotor areas, right and left insula and Broca's area, is recruited for the processing of novel metaphors but not for the processing of conventional metaphors.